The next-generation BMW Z4 roadster is slated to arrive in 2015, and according to new reports, it's going to be a more dynamic machine. Well, slightly more dynamic, since the Z4 will still need to squeeze into the triangulated space between better driving chops and not looking too different than the current car. Buyers may want a better driver's car, but they also want a timeless design that will still look good in 15 years.